In a production step of semiconductors and chemical products, a variety of gasses are used and these gasses are supplied, for example, via a pipe from a gas container loaded with a high-pressure gas. In cases where the gas needs to be supplied continuously, plural gas containers are connected in parallel. When the residual pressure in one of the gas containers decreases to a preset lower limit, the gas supply is switched to another gas container and at the same time, the gas container in which the pressure decreased is replaced with a new gas container to be put on standby (for example, see Patent Document 1). Also, the amount of residual gas in each of the plural gas containers is detected to select a gas container having a low amount of the residual gas, which is used to supply the gas (for example, see Patent Document 2).